CVE-2023-42366: BusyBox Buffer Overflow Vulnerability

CVE-2023-42366 Overview

A heap-buffer-overflow vulnerability was discovered in BusyBox v.1.36.1 in the next_token function at awk.c:1159. This memory corruption flaw occurs during AWK script parsing and can be exploited through specially crafted input files to cause denial of service conditions. BusyBox is widely deployed in embedded systems, IoT devices, and Linux-based appliances, making this vulnerability particularly concerning for environments where system availability is critical.

Critical Impact

Attackers can trigger a heap buffer overflow through malicious AWK input, potentially causing application crashes and denial of service on affected BusyBox installations.

Affected Products

• BusyBox version 1.36.1
• Systems and embedded devices running vulnerable BusyBox AWK implementation
• IoT devices and embedded Linux systems utilizing BusyBox utilities

Discovery Timeline

• 2023-11-27 - CVE CVE-2023-42366 published to NVD
• 2024-12-06 - Last updated in NVD database

Technical Details for CVE-2023-42366

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically manifesting as a heap buffer overflow in BusyBox's AWK implementation. The flaw exists in the next_token function located in awk.c at line 1159. When processing specially crafted AWK scripts or input data, the function fails to properly validate buffer boundaries, allowing writes beyond the allocated heap memory region.

The local attack vector requires user interaction, meaning an attacker would need to convince a user or automated process to process a malicious AWK script or input file. While the vulnerability does not directly enable code execution or data exfiltration, successful exploitation results in application crashes, causing high availability impact.

Root Cause

The root cause of this vulnerability lies in insufficient bounds checking within the next_token function during lexical analysis of AWK input. The parser allocates a heap buffer for token processing but fails to properly validate the size of input data before writing to this buffer. When processing tokens that exceed expected lengths, the function continues writing past the allocated buffer boundary, corrupting adjacent heap memory structures and ultimately leading to a crash.

Attack Vector

The attack requires local access and user interaction to exploit. An attacker must craft a malicious AWK script or input file that triggers the overflow condition when processed by the vulnerable next_token function. Attack scenarios include:

1. Providing a malicious AWK script to a user for execution
2. Exploiting automated systems that process untrusted AWK files
3. Targeting embedded devices that use BusyBox AWK for data processing

The vulnerability can be triggered when BusyBox's AWK utility parses input containing specially constructed tokens designed to overflow the internal buffer. For detailed technical analysis, refer to the BusyBox Bug Report #15874.

Detection Methods for CVE-2023-42366

Indicators of Compromise

• Unexpected crashes or segmentation faults in BusyBox AWK processes
• Core dumps showing heap corruption in awk.c or related functions
• Unusual AWK script files appearing on the system with abnormally large or malformed content
• System logs indicating repeated AWK process failures

Detection Strategies

• Monitor for abnormal termination of BusyBox AWK processes using process monitoring tools
• Implement file integrity monitoring for AWK scripts in automated processing pipelines
• Deploy memory safety tools like AddressSanitizer during testing to detect heap overflows
• Review system logs for patterns of AWK-related crashes or segmentation faults

Monitoring Recommendations

• Configure alerting for repeated process crashes involving BusyBox utilities
• Implement centralized logging for embedded devices running BusyBox to detect crash patterns
• Monitor system stability metrics on IoT devices and embedded systems using BusyBox
• Establish baseline behavior for AWK script processing and alert on anomalies

How to Mitigate CVE-2023-42366

Immediate Actions Required

• Inventory all systems and devices running BusyBox version 1.36.1
• Restrict access to BusyBox AWK functionality where possible
• Implement input validation for any AWK scripts processed from untrusted sources
• Consider disabling AWK applet in BusyBox configurations where it is not required

Patch Information

Organizations should monitor the official BusyBox project for security updates addressing this vulnerability. The issue has been documented in BusyBox Bug Report #15874. NetApp has also published a related security advisory for affected products at NetApp Security Advisory NTAP-20241206-0007.

Upgrade to a patched version of BusyBox when available from the vendor. For embedded devices, contact the device manufacturer for firmware updates that include the patched BusyBox version.

Workarounds

• Disable the AWK applet in BusyBox builds if not required for system operation
• Implement strict input filtering for any files processed by BusyBox AWK
• Use alternative AWK implementations (gawk, mawk) on systems where feasible
• Apply principle of least privilege to processes invoking BusyBox AWK

For systems where BusyBox AWK cannot be disabled or replaced, consider implementing input validation to reject potentially malicious AWK scripts before they are processed. Review the BusyBox build configuration to minimize the attack surface by disabling unnecessary applets.